Trust me it is the real representation of gamuts. With a great advantage of being in linear space. I can't overemphasize that fact.
There is no need to go into nonlinear Lab gamuts, such as those in the commercial programs presented here. In fact, though I could be wrong, and I have to verify my findings, but there is an issue of gamut being twisted in those programs but I was afraid to point that out. Because if I did, Digital Dog will be all over me, saying "how come you are right and these established tools have the possibility of being incorrect?"
I am totally open to new findings. If you are right: fine so. Then we've learnt a lot!
My problem is I have no clue (well, little) about the physics and maths behind all that stuff. But as a (not totally unexperienced) "user" I can't replicate your findings and it is also not in line with my understanding of color mapping / color appearance.
So, down to earth...:
I can create high saturated AdobeRGB blues (source) that clip in ProPhoto (target) when I convert
abscol from AdobeRGB to ProPhoto (because, well, D65 light is "bluer" than D50 light).
But the inverse "test" doesn't work: all the blues (from the highest saturated blue to almost white) in ProPhoto (source) clip when I convert to AdobeRGB (target)... relcol or abscol, either way. How so... when your findings are right?